1. Field of the Invention
The present invention relates to an image pickup apparatus capable of acquiring an image of an object in gas and liquid, and a method for operating the image pickup apparatus.
2. Description of the Related Art
Some image pickup apparatuses not only pick up an image of an object existing in gas such as air but also pick up an image of an object existing in liquid such as water.
For example, in Japanese Patent Application Laid-Open Publication No. 2007-318533, a digital camera capable of performing stroboscopic photographing in water by being accommodated in a waterproof pack is described. However, a lens portion is configured larger in a case of a waterproof pack of a lens projection type digital camera, and, therefore, when stroboscopic photographing is performed with a built-in strobe, strobe light is blocked by the lens portion, and vignetting occurs. Therefore, Japanese Patent Application Laid-Open Publication No. 2007-318533 proposes a technique in which whether an underwater photographing mode is set or not, and, if it is judged that the underwater photographing mode is set, image processing for correcting an image where vignetting by strobe light has occurred to an image without the vignetting is performed.
Further, in Japanese Patent Application Laid-Open Publication No. 2010-35131, a technique is described in which, when a conversion lens is fitted to a digital camera, vignetting caused by the conversion lens is detected. More specifically, in Japanese Patent Application Laid-Open Publication No. 2010-35131, image data is separated longitudinally and laterally to divide the image data into areas with an appropriate size; an exposure value in each area is measured to calculate an evaluation value; and it is detected that vignetting has occurred in the image data if such an evaluation value pattern that evaluation values around the image data are values indicating black is detected.